1. Field of the Invention
Fiber reinforced resin composite structures are used in the manufacture of parts and finished goods in automotive, recreation vehicle, trucking, aerospace, marine, rail, appliance, athletic equipment, container, construction, anti-corrosion, electrical and medical industries. The present invention relates generally to closed molded resin infusion and resin transfer molding techniques for the production of fiber reinforced resin plastic (composite) structures in these and other industries. More specifically it relates to the use of three-dimensional spacer fabrics in resin infusion and resin transfer molding processing of fiber reinforced plastics as part of or all of the composite laminate to act as both as an INTERLAMINA INFUSION MEDIUM that significantly improves the speed (by 200% to 400%), uniformity and ability to quality-control the transfer, delivery and distribution of matrix resin (plastic) throughout the laminate stack with utility far beyond any other product or process in prior art or on the market and as a REINFORCING COMPOSITE LAMINA that dramatically improves mechanical and structural properties in the finished composite part as applied to the manufacture of parts and finished goods in the aforementioned and other yet-to-be identified industries. It also relates to the use of three dimensional spacer fabrics as surface infusion media for the purposes of improving upon the prior art in surface vacuum infusion, described in greater detail below.
2. Description of the Prior Art
Open Molded Laminating Techniques
A typical open mold process for constructing these parts consists of laying or placing either dry fibers or previously resin-impregnated fibers (also known as “pre-pregs”) into an open mold of the desired shape. Dry fiber reinforcements are saturated with liquid resin using manual techniques such as hand wet-out or spray application (processes commonly referred to as hand/contact lay-up and spray lay-up, respectively), which are then allowed to cure to form. Once placed in the open mold, pre-pregs are simply allowed to cure to form. When a flexible vacuum bag is applied to the part during the curing stage of these traditional open molding processes, atmospheric pressure can provide a slight improvement in the consolidation of the laminate prior to curing (this modification is sometimes referred to as “wet-preg vacuum bagging”).
Benefits and Drawbacks of Prior Art in Open Molded Laminating
Open mold processing has relatively low start-up and implementation costs for limited-run or custom part production. The problems associated with open mold processing include: high emissions of volatile organic compounds; uneven distribution of resin within the fiber structure often resulting in over-saturated and/or under-saturated areas; formation of air voids and bubbles; and use of excess resin or waste of resin in the process. Furthermore, open molding unit production costs are relatively high due to the labor-intensity and limited throughput.
Closed Molded Resin Infusion Techniques
In closed mold processing, fiber and/or other reinforcement(s), collectively referred to as the “pre-form,” are cut to fit then placed in the mold. A method of enclosing and compressing the pre-form against the mold is then employed. Resin is introduced into the pre-form by ports through the enclosure. Upon resin curing the enclosure is first removed, followed by the finished part. There are two principal closed molded resin infusion techniques commonly used to enclose and compress the pre-form against the mold, and to distribute resin through the pre-form:
VACUUM INFUSION uses one hard, rigid mold and one flexible bag or membrane that when joined are sealed to form a “closed” mold. Typically before applying the flexible bag or membrane a disposable barrier layer commonly referred to as a peel ply is placed on top of the pre-form. A peel ply allows resin to pass through it but will not stick to the resin once it is cured. A disposable infusion medium and/or perforated injection tubing is then placed on top of the peel ply to aid in the delivery and distribution of the liquid resin down through the laminate stack. In the case of a reusable vacuum bag or membrane the distribution channels may be incorporated into the bag. Vacuum pressure is then applied and draws resin through feed-lines into the mold and through the fiber pre-form. This technique is commonly referred to as surface vacuum infusion processing since the resin is introduced at the top surface of the laminate, which is described in Seeman et al. U.S. Pat. No. 5,052,906, 4,902,215 and 5,601,852.
RESIN TRANSFER MOLDING uses two hard, rigid molds that when joined are sealed and form an open cavity into which liquid resin is introduced. The resin can be introduced with or without the aid of vacuum or applied pressure.
Combinations and variations of vacuum infusion, resin transfer molding and other techniques can also be employed and will be known to those familiar with the state of the art.
Benefits and Drawbacks of Prior Art in Closed Molded Resin Infusion:
A number of benefits can be derived through the use of vacuum infusion vis-a-vis open molding and resin transfer molding techniques. Compared to open molding, labor requirements can be reduced and the rate of production from each mold can be improved. For example, labor involved in rolling out air bubbles and distributing the resin is reduced since the vacuum helps to improve the distribution of resin throughout the pre-form. Vacuum infusion also helps to maintain more consistent resin-to-glass ratios by providing the fabricator with the ability to more precisely control the resin input. Product quality and strength are improved since the vacuum removes trapped air and serves to insure tight bonding of all materials in the lay-up. Compared to resin transfer molding, vacuum infusion requires less set-up time and has much lower tooling costs. Additionally, resin transfer molding has the inherent risk of fiber washout or fiber movement/displacement due to resin flow, as well as resin racing or non-wetting in areas of complexity or varying part thickness. The greatest drawback of surface vacuum infusion is high waste and non-profit stream costs in the disposal of peel plies and surface infusion media. Surface vacuum infusion also has an inherent risk of resin pooling in low-lying areas due to loss of vacuum pressure after the passage of the resin flow front.
In these respects, the use of THREE-DIMENSIONAL SPACER FABRIC INTERLAMINA INFUSION MEDIA AND REINFORCING COMPOSITE LAMINA to aid in the transfer, delivery and distribution or resin according to the present invention substantially departs from the conventional concepts and designs of the prior art, and in so doing provides a technique and a material primarily developed for the purpose of increasing the resin distribution rate and uniformity throughout the lay up while improving mechanical properties.